Pineapple drying using a new solar hybrid dryer

This paper presents the results of an experimental pineapple (Ananas comosus L.) drying study in a new solar hybrid dryer. The dryer is a direct and integrated type, with a black mate pan which measures 1.675 x 0.61 x 0.055 m (1.02 m(2)). It uses a copper helical tube that conducts hot water, at 80 degrees C, generating extra heat for the drying process; the tube is located at the bottom of the black pan. A caliber 6, transparent vinyl film is used as a cover and the walls and base of the dryer are isolated by 0.0254 m thick fiberglass. It is inclined 23 degrees south and uses pump to recirculate water. The variety of pineapple used was honey, 1/4 of grown age. Each slice was 0.005 m thick, resulting in a mass density of 2.83 kg/m(2) in the drying trays area. To be able to have useful comparisons, drying tests were performed during winter and spring of 2013, using both the hybrid dryer and the traditional solar dryer. Results showed that when initial humidity between pineapples is quite similar (this being one of the most influential factors in changing efficiency, time and other important process variables), evaporation efficiencies are higher in the traditional process; such efficiencies ranging between 22.7% and 24.0%; while the efficiency of the hybrid dryer ranges between 9.3% and 14.0%. This is basically due to the increase of energy loss when using both sunlight and heated water. On the other hand, the time the process took to reach the humidity goal (24.0% humid base or 0.32 dry based) was much faster when using the hybrid dryer. This dryer ended the process in a range of 6.0 to 6.8 hours while the traditional solar process took between 8.0 and 8.8 hours. It is also important to note that the final process was basically homogeneous throughout the dryer, especially when the drying trays on the top end of the dryer were placed 0.03 m further away from the top, and produced a fine quality product with only slight discoloration of the pineapples' side which faced the sun. (C) 2014 The Authors. Published by Elsevier Ltd.